This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-29642 filed Feb. 6, 2001.
The present invention relates to a load control apparatus and method with a plurality of switching components for driving a plurality of electrical loads.
A vehicle has various electrical loads including lamps and motors, and a load control apparatus with high current output capability to drive these loads. In a conventional load control apparatus, molded MOS power transistors with self-protection functions are mounted. If an excessive current flows due to a short in one of the loads, the power MOS transistor generating abnormal heat as a result of the excessive current is turned off. Therefore, an abnormal condition of one load has no impact on driving other loads.
However, the load control apparatus has limitations in terms of the size. Since each power MOS transistor included in the load control apparatus has a molding and is mounted on a printed circuit board, decreasing the size of the transistor is very limited, namely, decreasing the overall size of the load control apparatus is limited. As a result, it takes up a large portion of interior space of a vehicle. Moreover, the power MOS transistors with a self-protection function are very expensive. Therefore, cost issues become critical, especially when more power MOS transistors are required for more loads.
The present invention therefore has an objective to provide a relatively small and cost-effective load control apparatus and method that can protect a switching component causing abnormal heat generation.
According to the present invention, a load control apparatus detects heat generated by switching components by a single temperature detection circuit provided generally equidistantly from the switching components. Therefore, it is able to detect every temperature increase due to heat generation in any one of the components.
Preferably, the load control apparatus detects a current flowing in each switching component. If the load control apparatus has detected abnormal heat generation based on the detected temperature, it identifies which switching component generates the abnormal heat based on the detected current of each switching component. Then, it performs a protection control to the identified component. Therefore, the switching component generating an abnormal heat can be exclusively controlled to protect other components.
Since only one temperature detection circuit is required for a plurality of switching components, it is cost-effective. It is not necessary to integrate a switching component, a temperature detection circuit, and a current detection circuit into one chip. Therefore, the load control apparatus can be smaller in size than conventional load control apparatus.